States, I guess. Now to do the others

Game states are named and used to toggle behavior. Now to rewrite those
things to do the *right* behavior.

src/lib.rs

@@ -11,7 +11,7 @@ impl Plugin for AsteroidPlugin {
     fn build(&self, app: &mut App) {
         app.add_systems(
             Startup,
-            (spawn_camera, spawn_player, spawn_ui, start_screen),
+            (spawn_camera, spawn_player, spawn_ui),
         )
         .insert_resource(ClearColor(BACKGROUND_COLOR))
         .insert_resource(WorldSize {
@@ -22,15 +22,29 @@ impl Plugin for AsteroidPlugin {
         .insert_resource(Score(0))
         .add_systems(
             FixedUpdate,
-            (input_ship_thruster, input_ship_rotation, wrap_entities),
+            (input_ship_thruster, input_ship_rotation, wrap_entities).run_if(in_state(GameState::Playing)),
         )
         .add_systems(
             FixedPostUpdate,
-            (integrate_velocity, update_positions, apply_rotation_to_mesh),
+            (integrate_velocity, update_positions, apply_rotation_to_mesh).run_if(in_state(GameState::Playing)),
+        )
+        .add_systems(
+            OnEnter(GameState::TitleScreen),
+            start_screen
         );
+
+        app.insert_state(GameState::TitleScreen);
     }
 }
 
+#[derive(Clone, Debug, Eq, Hash, PartialEq, States)]
+enum GameState {
+    TitleScreen,    // Program is started. Present title screen and await user start
+    GetReady,       // Short timer to let the player get ready after pressing start
+    Playing,        // Player has started the game. Run the main loop
+    GameOver,       // Game has ended. Present game over dialogue and await user restart
+}
+
 #[derive(Component)]
 struct Position(bevy::math::Vec2);